This slide furnish a detailed overview on the topic of solid state chemistry. These slides will also provide a basic understanding on solid state chemistry.

1. SOLID STATE CHEMISTRY-
Overview
Dr.P.Meenakshi
Assistant Professor
Department of Chemistry

2. Matter
Liquids
Gases
Solids
Fluids (easy tomove)
•Solids havefixed positions.
• Canoscillate abouttheirmeanpositions.
• This explains therigidityof molecules
THE SOLID STATE

3. Characteristics of Solid State:
•Solids have definite mass, volume and shape.
•Short intermolecular distance.
•Strong intermolecular forces.
•Constituent particles have fixed positions (oscillate about their mean
positions).
•Solids are incompressible and rigid structure.
THE SOLID STATE – General Characteristics

4. ClassificationofSolidsandCrystallineSolids:
Constituent Particles
Molecular Solids
Ionic Solids
Metallic Solids
Covalent Solids
Solids
Amorphous solids
Crystalline Solids
Molecules
Ions
Metals with Positive
ions surrounded bysea
ofelectrons
Non-metals with
covalent bonds
THE SOLID STATE – Types of Solids

5. Types ofMolecular Solids:
•Non-polarMolecularSolids:
•Compriseeitheratoms(Ar, He) ormolecules formedbynon-ploarcovalentbonds(H2, Cl2,I2).
•Attractedbyweakdispersionforces(or) Londonforces.
•Softin natureandnon-conductorsofelectricity.
•Lowmelting point(Gas andliquids atroomtemperature(or) pressure)
•PolarMolecularSolids:
•Molecules formedbypolarcovalentbonds.(Eg: HCl , SO2,etc…)
•Strongdipole-dipole interactionbetween themolecules.
•Softandnon-conductorsofelectricity.
•Higher melting pointsthanthenon-polarmolecularsolids.(Eg: SolidSO2 andSolidNH3)
• Most ofthemareliquids andgases atroom temperatureandpressure.

6. Types of Molecular Solids:
• Hydrogen Bonded Molecular Solids:
• Molecules contain polar covalent bonds between H and F, O or N atoms.
• Strong hydrogen bonding between the molecules. (Eg: H2O-ice).
• Non-conductors of electricity.
• Volatile liquids (Or)Soft solids at room temperature and pressure
.
Ionic Solids:
• Ions are constituent particles.
• Solids formed by three dimensional arrangementof cations and anions- strong coulombic
forces.
• Solids are hard and brittle in nature with high melting and boiling points.
• Electrical insulator in solid form (In molten state , these solids conduct electricity).

7. Metallic Solids:
• Orderly arrangedmetals (Positive ions surrounded by sea of free electrons).
• These electrons are mobile and freely moved throughout the crystal.
• High thermal and electrical conductors (duetofreeandmobileelectrons).
• Metals are highly malleable and ductile in nature.
Covalent (or) Network Solids:
• Non-metals formed by the formation of covalent bonds between adjacent atoms.
• Also called “GiantMolecules”.
• Strong covalent bonds and directional in nature.
• These solids are very hard and brittle.
• Extremely high melting points and Insulators (donotconduct electricity).Eg:Diamond & Silicon
Carbide.
• ExceptionalCase: Graphite. (Soft and electrical conductors).

8. Crystal Lattices:
•Regularthreedimensional arrangementof points in space.
Unit cell:
•Repetition of small portion crystal lattice indifferent directions to generateentirelattice
THE SOLID STATE – Crystal Lattices & Unit Cells

9. Classification ofunit cells:
•Primitive Unit cells:
•Constituentparticlelocated onlyon thecornerpositionsofunit cell.
• Centred Unitcells:
•oneormoreconstituentparticlespresent atpositionsotherthancornersin additiontothoseatcorners.
 Body-Centredunitcells: Oneconstituentparticleatitsbody-centrebesidesthe oneatcorners.
 Face-Centredunitcells:One constituentparticle presentatcentre ofeach face+one thatatall the
corners.
 End-Centredunitcells:One constituentparticlepresentatthe centre ofanytwooppositefaces+ one
presentatits corners.
THE SOLID STATE – Crystal Lattices & Unit Cells

10. Seven Crystal Systems:
Crystal
System
Examples
Simple Cubic NaCl, Zinc blende,
Cu
Tetragonal White tin, SnO2,
TiO2
Orthorhombic Rhombic Sullphur,
BaSO4
Hexagonal Graphite, ZnO, CdS
Rhombohedral
/ Trigonal
Calcite (CaCO3),
Cinnabar (HgS)
Monoclinic Monoclinic Sulphur,
Na2SO4.10H2O
Triclinic K2Cr2O7,
CuSO4.5H2O, H3BO3
THE SOLID STATE – Crystal Lattices & Unit Cells

11. BravaisLattices:
THE SOLID STATE – Crystal Lattices & Unit Cells

12. Numberofatoms in a UnitCell:
•Primitive Cubic unit cell:
•Atoms only at a centre. (Shared by eight adjacent unit cells).
8corner* 1/8of an atom
= 8*1/8=1atom
Eachcornersharedby1/8ofanatom.
THE SOLID STATE – Closed Packed Structures

13. Numberofatoms in a UnitCell:
•Body-Centred Cubic unit cell:
• Unitcell with an atom at eachof its corners and also one atom at its body-centre.
1wholeatomatcentre
1/8atomat8corners
1wholeatomatcentre+1/8ofanatomat8corners
1 Atom+(8*1/8ofanatom)=1+1= 2atom
THE SOLID STATE – Closed Packed Structures

14. Numberofatoms in a UnitCell:
•Face-Centred Cubic (fcc)unit cell:
•Unit cell with an atom at each of its corners andat the centre of all faces of the cube.
• Each atom in face centre is shared by2 adjacent unit cells. (6faces*½ofanatom)
• Each atom at corners is shared by 8 adjacent unit cells. (8corners *1/8ofanatom)
1/8of anatom*8corners
1/2of anatom*6faces
½ofanatomat6faces +1/8ofanatomat8corners
(6*1/2ofanatom)+(8*1/8ofanatom)=3+1= 4atom
THE SOLID STATE – Closed Packed Structures

15. Close PackedStructure:
•Constituentparticlesareclose-packedbyleavingaminimumvacantspace.
• Close Packing in one-dimension :
•Close Packing in two-dimension:
•Generatedbystackingtherowsofclose packedspheresintwo differentways.
• Secondrowisplacedexactlyon firstrow.(AAAtype)
•EachSphereis incontactwithtwoofitsneighbours.
• NumberofneighbouringatomsisthecoordinationNumber.
• Thecoordinationnumberofclosepackingstructureis “2”.
• Each Sphereisincontact with4neighbouring
atoms.
• CoordinationNumber= 4.
• Joiningthecentresof4immediatespheresgiverise
tosquareshape.
• Thispackingiscalledas“squareclose packingin
twodimensions”
THE SOLID STATE – Closed Packed Structures

16. Close Packing in twodimension:
• Second rowis placed above firstrowin a staggered manner (i.e) sphere fits in the
depressions offirst row.
• Arrangement of firstrow sphere is termed as “Atype”.
• Arrangement ofsecond rowsphere is termed as “B type”
.
• This type arrangement is termed as “ABAB” type.
• This arrangement has less free space andmorepacking efficient than square close packing.
• Each sphere is in contact with six of its neighbours andthe two dimensional
•coordination number is “Six”.
• Joining ofcentres of6 neighbouring spheres give rise to
hexagonal shape. Hence this packing arrangement is known as
“two dimensionalhexagonal closepacking”.
• The voids(emptyspaces)aretriangular inshape. These triangular
voids areof two types. In one rowapex is pointing upwards
And in second rowthe apex oftriangleis pointing downwards.
THE SOLID STATE – Closed Packed Structures

17. Close Packing in three dimensions: Stackingof two dimensional layersone above the other.
•Threedimensional close packing formstwo-dimensional square close-packedlayers:
•Placing second square close -packedlayer above the first layer.Thesphere of upper layeris exactly above the first layer
.
•Spheresof both layersareperfectly aligned horizontally as well as vertically.
•If thearrangement of first layeris “A type”and all thelayershave same arrangement,then thepattern is termedas “AAA
type”.
•Thelattice is a simple cubic lattice and its unitcell is Primitivecubic unitcell.
THE SOLID STATE – Closed Packed Structures

18. Close Packing in three dimensions: Stackingof two dimensional layersone above the other.
•Threedimensional close packing formstwo-dimensional hexagonal close-packed layers:
a. Placingsecond layerover thefirstlayer:
• First layerof two dimensional hexagonal close packedlayer(A) is overloaded by thesecond layerof two
dimensional hexagonal layerat the depressions of first layer(B).
• All the triangularvoids of first layerare not covered by sphere. This give rise to different arrangements.
• Tetrahedral voids: Sphereof second layeris above the void of the first layer.
• voids formedare called “Tetrahedral voids”.
• Tetrahedron is formedwhen the centres of four spheres
are joined.
TetrahedralVoids
Sphereof firstlayer
Sphereof secondlayer
THE SOLID STATE – Closed Packed Structures – “VOIDS”

19. OctahedralVoids: Triangularvoidsin thesecondlayerareabovethe triangularvoidsin thefirstlayer.The
triangularshapesoftwolayersdo notoverlap.
•Apexon onetriangleis pointing upwardsandthe apexofanothertriangleis pointingdownwards.
•Suchvoidsaresurroundedbysix spheres andaretermed as“OctahedralVoids”.
Triangle apex pointing downwards
Triangle apex pointing upwards
OctahedralVoids
THE SOLID STATE – Closed Packed Structures – “VOIDS”

20. b.Placingthethirdlayeroverthesecondlayer:
Whenthe thirdlayeris placeover thesecondlayer,twoarrangementsarepossible.
 Coveringtetrahedralvoids:
 Tetrahedralvoidsofsecondlayerarecoveredbythe spheresof thirdlayer.
 Spheresofthirdlayerareexactlyarrangedwith thoseoffirstlayer.
 Patternis repeatedalternatively.Itis termedas “ABAB...”.
 This structureis called as“hexagonalclosepacked(hcp)structure.”
 Eg:Metals likemagnesium andZinc.
A
B
A hcp Structure
THE SOLID STATE – Closed Packed Structures –
“hcp Structure”

21.  CoveringOctahedralVoids:
Thirdlayeris placed abovethe secondlayerin a mannerthatits spherescover theoctahedralvoids.
In thistypearrangementthethirdlayerspheres arenotalignedwith neitherfirstlayernorsecond
layer.So,thirdlayeris termedas“C”.
This patternis termedas “ABCABC...”.Thisstructureis called as“CubicClosePacked(ccp)or
Face-centredCubic(fcc)Structure”.
Eg:Metalssuch ascopper andSilver crystallisein thisstructure.
Bothhcpandccphasacoordinationnumberas“Twelve”.
A
C
B
A
Cubic Close Packed(ccp)
Structure
THE SOLID STATE – Closed Packed Structures –
“ccp Structure”

22. Locating Tetrahedraland OctahedralVoids: Close packedstructureshave both tetrahedral and Octahedral voids. A unitcell
of ccpor fcc structureunit cell.
Locating of tetrahedral voids:
•Theunit cell is divided into eight small cubes.
•Each small cube has 4 atoms. Joining4atoms giverise to “Regular Tetrahedron”.
•One tetrahedron void ineach small cube. So eight small cubehas eight tetrahedron void in total.
•ccp Structure has 4 atoms per unit cell.
•Thenumberof tetrahedral voids is twice the number of atoms.
Tetrahedron voids
THE SOLID STATE – Closed Packed Structures

23.  Locating of Octahedral Voids:
• The body centre ofthe cube is surrounded by 6 atoms in face centres. On joining these face centres – Octahedral void.
• Another Octahedral void at the centre ofeach ofthe 12 edges.
• It is surrounded by 6 atoms (4 belonging tosame unit cell &2 belonging totwo adjacent unit cells).
• Each edge ofthe cube is shared between four adjacent unit cells.(Octahedral void)
• Only ¼ th ofeach void belongs toa particularunit cell.
Octahedralvoids atbody centreof cube= 1
12octahedralvoids (atedge)sharedbetween4unitcells= 12* ¼ = 3
TotalNumberof octahedralvoids = 4
Inccp structure,eachunitcellhas4atoms.
TheNumberofoctahedralvoids is equaltotheNumberof
an atoms”.
THE SOLID STATE – Closed Packed Structures

24. PackingEfficiency:Percentage oftotal space filled by the particles.
Calculationofpackingefficiencyindifferenttypesofstructures:
Hcp andccpstructures: Both ccp andhcp structures areequally efficient. Consider ccpstructure for acalculation.
A
B
F
G
a
C
D
b
H
E
a
∆ABC, AC2 =AB2 +BC2 ; b2 =a2 +a2 =2a2 ; b2=2a2; b=√2a
If ‘r’ is a radius ofa sphere, then b=4r= √2a
r
r
a 2
2
2
4


2
2
a
r 
• Each unitcellhas4atoms(spheres)
• Totalvolumeof4spheres=4*(4/3)Π r3
• Volume ofcube= a3 (or) 3
)
2
2
( r
PackingEfficiency= Volume occupiedby 4 spheresinunit cell * 100%
Totalvolume of theunit cell
=4* (4/3)Π r3*100%
3
)
2
2
( r
= 74%
THE SOLID STATE – Packing Efficiency

25. Packing Efficiencyin Body-CentredCubicStructures:
c
H
G
F
E
D
C
B
A
a
b
a
a
In ∆EFD, FD2=FE2+ED2; b2=a2+a2= 2a2 ;
a
b 2

In ∆AFD, AF2=AD2+DF2; c2=a2+b2= a2+2a2 ; a
c 3

Length ofbody diagonal ‘c’=4r. All spheres arealongthe diagonal
r
a 4
3 
3
4r
a  a
r
4
3

No. Of atoms in bccstructure= 2
Volume= 3
3
4
*
2 r






 Volume ofcube=
3
3
3
4






 r
a
PackingEfficiency= volumeoccupiedby 2spheresinunitcell*100
Totalvolumeofunitcell
%
 
 
 
%
3
/
4
100
*
3
/
4
*
2
3
3
r
r

= = 68%
THE SOLID STATE – Packing Efficiency

26. PackingEfficiencyinSimpleCubicLattice:
Particlestoucheachotheralongtheedge;Edge length(or)sideofthecube=‘a’;radiusofeachatom= r ; a=2r
Volume ofcubic unit cell= 3
3
3
8
)
2
( r
r
a 
 Simple cubic contains 1 atom in unit cell.
Volume ofasphere = 3
3
4
r

Packing Efficiency =Volume of an atom
Volume of cubicunit cell
*100%
100
*
6
100
*
8
3
4
3
3



r
r
= = 52.4%
C
B
A
H
G
F
E
D
THE SOLID STATE – Packing Efficiency

27. Imperfections inSolids: Basic irregularitiesin the arrangementof constituent particles.
•Two types of defects = Point defects and Line defects.
•Point Defects: Irregularitiesinarrangementarounda point or an atom in crystallinesubstance.
•Line Defects: Irregularitiesfrom ideal arrangement in entirerows of the lattice points.
TypesofPoint Defects:
Stoichiometric Defects.
ImpurityDefects.
Non-Stoichiometric Defects.
Stoichiometric Defects:
 Do not disturb thestoichiometry of thesolid.
 Also called ‘Intrinsic Defects’ or ‘Thermodynamic defects’.
 Two types : VacancyDefects and Interstitial Defects.
THE SOLID STATE – Point Defects

28. VacancyDefects:
Crystalwithvacantlatticesites.
Resultsin decreasein densityofthesubstance.
 This defectmayalsodevelop whenthe substanceis heated.
InterstitialDefects:
•Someconstituentparticlesget occupied in aninterstitialsite.
•This defectincreases thedensityof thesubstances.
Vacant lattice
sites
Interstitial Defects
Vacancy Defects
THE SOLID STATE – Point Defects

29. VacancyandInterstitialdefectsarealso shownbyionicsolids.
•IonicSolidsmaintainthechargeneutrality.
•IonicsolidsalsoshowstwodefectsnamelyFrenkel DefectsandSchottkyDefects.
Frenkel Defect:
•This defectisshownbyionicsolids.
•Smallerion (usuallycation)isdislocatedfromitsnormalsitetoan interstitialsite.
•Creatingvacancysiteatoriginalsite andaninterstitialdefect atitsnewlocation.
•Also called‘Dislocationdefect’. Doesnotchangethedensityof thesolid.
•Ionicsolidswithlargedifferencein sizeof ions.
•Eg:ZnS,AgCl, AgBr,AgI duetosmall sizeofAg+ andZn2+ ions.
THE SOLID STATE – Point Defects

30. SchottkyDefect:
•It is avacantsitein ionic solids.
•The numberofanionsandcationsareequaltomaintaintheelectrical neutrality.
•Decreases thedensityofthe substances.
•This defectis shownbyionic solids withsamesize ofanionsandcations.
•Eg:NaCl,KCl,CsCl andAgBr.
Vacancy site at original site
Interstitial site atnew site
Frenkel Defect Schottky Defect
THE SOLID STATE – Point Defects

31. ImpurityDefects
 Molten NaCl contains small amountof SrCl2 when crystallizes. Some sites of Na+ ions are
occupied by Sr2+.
 One site occupied and other get vacant.
 Cationic vacancies are equal in number to Sr2+ ions.
 Another example is solid solution of CdCl2 and AgCl.
Na+
Na+
Cl-
Na+
Na+
Sr2+
Na+
Na+
Cl-
Cl- Cl-
Cl-
Cl-
Cl- Cl-
THE SOLID STATE – Point Defects

32. Non-StoichiometricDefects:
 MetalExcess Defect
a. Metal ExcessDefect dueto anionicvacancies:
• Alkylhalides(NaCl andKCl) showthistypeofdefect.
• When crystals of NaCl heat in the atmosphere of Na vapours, The Na atoms are deposited on
surfaceofthecrystal.
• Cl- ions diffuse to surface of crystal and combine with Na atoms to give NaCl. The electron release
fromNaatomdiffusesintothecrystalandoccupytheanionicsites.
• Anionicsitesoccupiedby unpairedelectrons=F-centres.
e- F-Centre
THE SOLID STATE – Point Defects

33. b.Metal Excess defectduetothe Presence of extra cations at Interstitial Sites:
• On heating , ZnO loses its oxygen andturns yellow.





 
 e
O
Zn
ZnO heating
2
2
1
2
2
• Excess of Zn in crystal forms andthe formula becomes
• Excess Zn2+ ions move tointerstitial sites while the electrons move tothe neighbouring interstitial sites.
 MetalDeficiency Defect:
• Typical example is FeO. Mostly found composition is
• Composition ofFeO varies from O
Fe 95
.
0
O
Fe 93
.
0 to O
Fe 96
.
0
THE SOLID STATE – Point Defects

34. ElectricalProperties ofSolids:
Solids are classified into threecategories based on electrical its conductivity.
•Conductors
•Semi-conductors
•Insulators
o Conductors:
•Solids with conductive range between 104 to 107 ohm-1m-1.
•Metals haveconductivity in therange of 107 ohm-1m-1.
•Metals are good conductors of electricity.
o Semi-Conductors:
•Solids with conductivity inthe intermediate rangefrom
10-6 to 104 ohm-1m-1.
o Insulators:
•Solids with verylow conductivities inthe rangebetween
10-20 to 10-10 ohm-1m-1.
THE SOLID STATE – Electrical Properties

35. MagneticProperties:
Substances areclassified into 5 categories based on the magnetic properties:
 Paramagnetism:
•Paramagnetic substances are weaklyattracted by a magnetic field.
•Magnetised ina magnetic field in same direction.
•Presence of one or moreunpairedelectron attracted by the magnetic field.
•Eg: O2, Cu2+, Fe3+, Cr3+.
 Diamagnetism:
•Diamagnetic substances areweakly repelled by a magnetic field.
•Weakly magnetised ina magnetic field inopposite direction.
•All electrons are paired and no unpairedelectrons are found.
•Pairing of electrons cancels their magnetic moments andlose
their magnetic character.
•Eg: H2O, NaCland C6H6.
THE SOLID STATE – Magnetic Properties

36. Ferromagnetism:
• Thesesubstancesareattractedvery stronglybya magneticfield.
• ferromagnetsarepermanentlymagnetised.
•Metal ions offerromagneticsubstancesaregrouped intoasmall regions called “Domains”.
•Thesedomainsactsasasmall magnets.
•when substanceis placed in amagneticfieldall thedomainsget orientedin thedirection ofmagneticfield
andstrongmagneticfieldis produced.
•Theorderingofdomainscontinuestoexist even themagneticfield is removed andtheferromagnetic
substancesbecomes permanentmagnet.
THE SOLID STATE – Magnetic Properties

37. Antiferromagnetism:
•Thedomain structureis similar to ferromagnetic substance.
•But their domains areoppositely oriented and cancel out each other’s magnetic moment.
•Eg: MnO.
Ferrimagnetism:
•Magnetic moments of the domains in the substances arealigned inparallel and anti-parallel directions in unequal
numbers.
•Weakly attracted by magnetic field as compared with ferromagnetic substances.
•looses ferrimagnetism onheating and become paramagnetic on heating.
•Eg: Fe3O4 (magnetite) and ferrites likeMgFe2O4 and ZnFe2O4
Antiferromagnetic
ferrimagnetic
THE SOLID STATE – Magnetic Properties